1. Field of the Invention
This invention relates to electric power-generating devices such as wind turbines and ocean current turbines, and more particularly to a method and apparatus for taking the mechanical output of a low rotational velocity high-torque wind or water turbine and converting that to 3-phase electrical power to a utility line.
2. Description of the Prior Art
Many electric power-generating devices, such as wind turbines and ocean current turbines, benefit from economies of scale, yielding lower costs for generated electricity with larger power generation per unit. This increase in power is often accompanied by a reduction in rotational velocity of the power-input shaft, resulting in a large increase in torque. Because electric generators require rotational velocities tens to hundreds of times greater than the rotational velocity of the input shaft, a speed-increasing gearbox is often applied between the power-input shaft and the generator.
The above-referenced Dehlsen, et al application Ser. No. 09/552,577 discloses a powertrain for wind turbines and ocean current turbines which consists of a large, input power shaft-mounted, rotating bull-gear with stationary smaller powertrains mounted around its periphery. The gear teeth on the bull-gear rotate past the teeth on the pinions, causing pinions to turn and deliver power to each smaller powertrain. Alternatively, powertrains are attached in a spindle around the perimeter of a main power input drive shaft, and rotate as the shaft rotates. The input drive shaft to each of the smaller powertrain gearboxes is fitted with a pinion. As the main power input shaft turns, the generators, gearboxes and pinions rotate, moving the pinions around the interior of a stationary ring gear. Reduction and distribution of torque is similar to the rotating bull-gear powertrain. In the bull-gear configuration, each smaller powertrain is stationary, reducing stress caused by rotation.
The power and control side of the powertrain must take the mechanical output from the individual second-stage gearboxes and produce 3-phase electrical power to a utility line. To perform successfully, this control system must assure a uniform torque load distribution between generators, smoothly connect and disconnect with the utility line, seek maximum operating efficiency, monitor and provide protection for mechanical and electrical parameters operating out of specification, and accommodate input from external systems and operators.
Therefore, besides generators, the power conversion system requires an appropriate controller to manage these tasks.
Briefly, the invention is concerned with a control method for use with an electric power-generating device that converts fluid flow of wind or water to electricity. The device includes a rotor having blades that rotate in response to fluid flow; a main power input shaft coupled to said rotor; a single-stage torque-dividing gearbox coupled to said main power input shaft; said torque-dividing gearbox having a plurality of output shafts located around a perimeter of said main power input shaft; and, a plurality of sub-powertrains, each one of said sub-powertrains including a generator coupled to a respective one of said torque-dividing gearbox output shafts, the control method comprising regulating torque experienced by each said generator to assure that torques are balanced between generators at any given system load.
In accordance with an aspect of the invention, the regulating step includes controlling local voltage at each said generator by a transformer configured as a reactor, in which coils of said transformers are wired in parallel and are actively modulated with an SCR, solid-state, switching device.
In accordance with another aspect of the invention, each generator is connected to a respective primary coil of a transformer and a respective secondary coil is connected to an SCR.